Without limiting the scope of the present invention, its background will be described with reference to operations performed in a subterranean well that traverses a fluid-bearing subterranean formation, as an example. Subterranean wellbores are generally filled with fluids that extend from the lower end of the wellbore to the earth's surface. During drilling and completions operations, a weighted column of fluid is usually present adjacent to each of the fluid-bearing formations intersected by the wellbore, so that the column of fluid may exert hydrostatic pressure on the formations sufficient to prevent uncontrolled flow of fluid from the formations into the wellbore, which uncontrolled flow of fluid could result in a blowout.
In order to transport fluid, tools, instruments and the like within the wellbore, it is common practice to utilize a tubular string, such as drill pipe or production tubing, to which tools and instruments may be attached and within which fluid may be flowed and tools and instruments may be conveyed. When such a tubular string is disposed within the wellbore, the fluid column within the wellbore may be effectively divided into multiple portions. For example, a first fluid column may be contained in an annulus defined by the area separating the outside surface of the tubular string from the inside surface of the wellbore or casing string. At the same time, a second fluid column may be contained within the interior of the tubular string. In such a configuration, tools, instruments and the like may be transported within the wellbore attached to or within the tubular string without disturbing the relationship between the fluid column in the annulus and the fluid-bearing formations intersected by the wellbore.
After completing the well, it is typically desirable to remove the weighted column of fluid from both the interior of the tubular string, if present, and the annulus above the uppermost packer. This may be achieved through the use of a circulating valve disposed within in the tubular string, which has a primary purpose of selectively permitting fluid flow between the interior of the tubular string and the annulus. For example, when it is desired to remove the weighted column of fluid from the annulus, a lighter fluid may be pumped from the earth's surface down through the tubular string and radially outwardly from the tubular string through the circulating valve into the annulus and then back to the earth's surface up through the annulus. Typically, such tubing conveyed circulating valves have a sliding sleeve that may be longitudinally shifted between circulating and non-circulating positions using wireline or slickline techniques. In the non-circulating position, conventional circulating valves typically utilize resilient materials such as elastomers for sealing between movable metal parts to prevent fluid communication between the interior of the tubular string and the annulus.
It has been found, however, that resilient sealing materials may deteriorate due to the harsh chemical, physical and thermal environment downhole. When such deterioration occurs, the seals may fail to prevent fluid communication between the interior of the tubular string and the annulus when a conventional circulating valve is in its non-circulating configuration. Accordingly, a need has arisen for an improved circulating valve that is operable to selectively permit fluid flow between the interior of the tubular string and the annulus. In addition, a need has arisen for such an improved circulating valve that does not rely on resilient sealing materials to prevent fluid communication between the interior of the tubular string and the annulus when the circulating valve is in its non-circulating configuration.